Emissions testing and maintenance of vehicles is effective if vehicle road conditions may be effectively simulated. This is typically accomplished by means of a roller arrangement for contact with drive wheels of the vehicle, with the rollers being operatively linked to a dynamometer for placing a controlled load on the rollers. The load quantum will be a function of the rotational speed of the rollers (i.e. the simulated vehicle speed), simulated and real friction losses, and a polynomial equation representing wind resistance of the particular vehicle. The dynamometer simulates two aspects of vehicle performance namely inertia and drag. Inertia in this case is governed by the weight of the vehicle and the equivalent of rotating masses of the vehicle, with the device thus simulating inertia based on this factor. Drag is simulated by the dynamometer applying a resistance to the rollers, governed by the actual wheel speed of the vehicle and the wind resistance factor, inertial energy may be provided by means of a fly wheel as well as simulation by other means.
Conventional roller testing stands for motor vehicles typically comprise one or more large rollers, with a single roller spanning the left and right vehicle wheels. For example, the apparatus disclosed in U.S. Pat. No. 3,554,023 (Geul); U.S. Pat. No. 5,154,076 (Wilson et al) and U.S. Pat. No. 5,193,386 (Hesse, Jr. et al), are all of this type. It is also known to provide a testing assembly for use with a motorcycle that contacts the sole driven wheel of the vehicle (U.S. Pat. No. 5,429,004--Cruickshank).
Conventionally dynamometer resistance is provided by a braking mechanism such as an electric motor, water brake, etc. However, other resistance-generating means may be employed and the present invention is not limited to the use of any particular braking means.
A chassis dynamometer may also be operated in reverse whereby the dynamometer rollers apply a force to the vehicle wheels and rotatably drive same. In this case, the dynamometer rollers are rotatably driven by a motor or the like and the force applied by the dynamometer is measured by a force sensor. In this configuration, the dynamometer may be used to test vehicle braking, transmission, or differential system functioning. For example, a brake test may be applied, wherein the chassis dynamometer is arranged to provide a steadily increasing power output to the dynamometer rollers, with the vehicle operator applying a corresponding increasing braking force to the vehicle brakes, until either brake failure is observed, wheel lock up is achieved or a preselected maximum value is reached.
Proper vehicle maintenance requires that the vehicle powertrain and brakes apply equal forces on both sides of the vehicle. However, it is often not sufficient to know simply that an imbalance exists, without having the imbalance quantified. It is desirable for a vehicle testing arrangement which employs a chassis dynamometer, to determine quantitatively the difference in force absorbed or transmitted between right and left and wheels, for a variety of vehicle systems. Thus, in the vehicle brake test described above, it is desirable to determine whether the right and left vehicle brakes (associated with right and left vehicle wheels) are applying a different force, and the quantitative value of any such difference. Similarly, when the chassis dynamometer is used in a power absorption mode, it is desirable to determine quantitatively any force output differential between the right and left hand vehicle wheels which might be indicative of mechanical problems in the vehicle differential.
It is also desirable to provide a portable chassis dynamometer assembly, which may be easily transported to a vehicle testing site such as a vehicle depot, and quickly and easily set up for carrying out vehicle emission performance tests. This eliminates the requirement of taking each vehicle separately to a dedicated test site. For this purpose, it is desirable to provide a chassis dynamometer testing assembly composed of individual subunits which may be separately carried and easily assembled on site without having to physically or mechanically link the subunits. The solution proposed by the present inventors is to provide individual left and right-hand roller dynamometer subunits, which may be simply placed on the ground at the wheel centers of the test vehicle. Such subunits may be electronically linked via a common control subassembly.
It is known to provide systems for testing vehicles with two or more driven wheels (i.e. wheels driven by the motor) comprised of individual left and right side roller assemblies. The rollers of such assemblies either share a common axle or are connected by a rail or frame spanning the roller pairs. See for example U.S. Pat. No. 5,193,386 (Hesse, Jr. et al.) and WO97/32189 (D'Angelo). Because of the large frame required in such arrangements, they do not provide a readily portable dynamometer arrangement that would permit easy transport and set-up. The assembly of such units at a test site would be time consuming and require specialized expertise. Such arrangements thus do not satisfy the need for a simple and easily transportable testing assembly, which is also simple to assemble for on-site testing use.
A further useful feature of vehicle dynamometers is that they be capable of centering the vehicle wheel on the rollers. This may be accomplished by providing paired frusto-conical rollers that each taper inwardly towards each other for supporting two opposing drive wheels (cf. Hesse Jr., et al.). In this arrangement, the vehicle is centered between the individual left and right-hand frusto-conical rollers. However, this arrangement requires that the right and left hand roller assemblies be either linked via a rigid frame or fastened to the floor, in order to prevent sideways slippage of the roller assemblies. Alternatively, the prior art discloses separate right and left hand rollers independently moveable on a common rail, and which may be locked in position when the rollers have been centered on the vehicle wheels (D'Angelo). However, this arrangement is still unsuitable for the use contemplated in this invention, in that it requires a large, rigid rail or frame joining the left and right hand rollers, which would be unsuitable for portable use. In order to achieve the objective of a simple, readily portable assembly, it is desirable to provide a simple means for centering a vehicle on the dynamometer assembly during operation of the device. In the solution proposed by these inventors, this is provided without any extraneous centering means, and in a manner consistent with the provision of left and right and roller subunits which rest on the ground.
It is also known to provide a logic circuit which independently controls front and rear roller sets for testing various front/rear vehicle load parameters such as attitude shift. See EPO 0 522 198 A1 (Yorikatso).
It does not appear to be known from the prior art, to provide a vehicle chassis dynamometer which is able to quantitatively determine the difference in vehicle power output or braking force, between the right and left side vehicle wheels. A quantitative determination of this type may be applied to the drive wheels (in the case of vehicle power output tests) and/or non-drive wheels (in the case of measurements of vehicle braking forces).
Conventional dynamometer-based testing devices are typically large, heavy and correspondingly expensive. This results in part from the provision of a single roller for contact with left and right driven wheels of a vehicle, that is wide enough for use with substantially all conventional vehicles, resulting in a large and heavy roller arrangement. This drawback may be addressed by providing a testing apparatus formed from separate left and right hand roller dynamometer sub-assemblies for individually supporting the vehicle drive wheels, with the sub-assemblies not being mechanically linked in order to provide for easy transport and assembly. The individual dynamometer assemblies are linked only electronically through a controller. The individual dynamometers may be thus in communication with a common control unit to equalize the simulated loads between the vehicle drive wheels. This arrangement also permits for unequal loads and wheel speeds between the individual units, to simulate a vehicle driving around a curve.